Argus analyst Philip Weiss cut his rating on the stock to hold primarily because of all of the unknown variables.

"We know that . . . BP's stock recovered 19% and outperformed the market and the sector following the Texas City refinery fire in 2005," Weiss says in a note to clients. (The Texas City refinery fire of 2005 was also at a BP-owned facility and resulted in 15 fatalities.) "However, we also think the level of environmental awareness and scrutiny is much greater now than it was at the time of those earlier accidents," he says.

There are plenty of technical reasons why BP may look like a buy right now, too.

"Both price-to-sales and price-to-cash earnings are very nearly at the low end of the historically normal range for BP," says Ned Douthat, head equity analyst at Ockham Research. "This valuation is likely appropriate given the huge downside potential given the cost of the spill. But if an investor wants to hold onto a stock for a long time, they could do worse than BP with a yield approaching 7%," Douthat wrote in an email.

Although Douthat doesn't think the risks associated with the spill are built into the stock yet, the price is starting to "become appealing in spite of the risk." Similarly, Philip Weiss of Argus said he would consider buying BP again if shares fell below $50.